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<br />Project Description and Alternatives <br /> <br />The purpose of this project is to provide a means for the PRBDC to continue providing irrigation <br />water to shareholders by replacing the existing siphon. <br /> <br />The current siphon was installed in the early 1950. It consists of a 32-inch steel pipe with a <br />side-wall thickness of about three-eights of an inch. The life expectancy of the siphon was <br />projected to be approximately 30 years. It has remained functional, with ever difficult and <br />increasing annual repairs, for twenty years beyond this projection. The outlet works of the <br />siphon streambed is layered with rust scales from two to four inches in diameter and up to an <br />eighth of an inch in thick. <br /> <br />Replacement of the siphon will require excavation of a trench to a depth of approximately six <br />feet. The trench will then be bedded with 6 inches of three-quarter inch minus washed granular <br />material. Then twenty-foot joints of a 30-inch diameter PVC pipe will be installed in the trench. <br />Before the pipe is covered with common material, the sides and top of the pipe will be covered <br />with three-quarter inch washed granular material to a thickness of approximately six inches. <br /> <br />Three options are being considered regarding the siphon alignment and associated trench <br />excavation. Option 1 includes removal of the old siphon and installing the new one in the same <br />alignment. Option 2 would be to excavate a trench adjacent to the old siphon, in virgin soil, a <br />distance of approximately six feet from the old alignment. Option 3 involves changing the angle <br />of the siphon at its mid point by approximately five to ten degrees to the south and establishing <br />a new discharge point approximately 100 to 200 feet down stream. <br /> <br />Advantages and disadvantages of each option are currently being evaluated and include the <br />following. <br /> <br />Option <br /> <br />Advantaaes <br /> <br />1. The new siphon will remain on the old established rights-of-way. The majority of the <br />east half of the old siphon is installed in a steep and very rocky slope. Installing the new <br />siphon in the old trench would eliminate the need and expense for blasting operations to <br />remove rock overburden to install the PVC pipe. <br />2. The surface of the ground at the center portion of the old siphon shows evidence of <br />boggy soils. Excavation of a trench adjacent to the old siphon could yield considerable <br />savings associated with eliminating the need to over excavate saturated material and the <br />purchase, hauling and backfill of other material to produce a solid foundation to lay the <br />new pipe on. <br />3. Installation of the east half of the new siphon would be on less boggy/saturated soils. <br /> <br />Option <br /> <br />Disadvantages <br /> <br />1. A higher probability exists with this option for increased costs associated with over <br />excavation of boggy /saturated soils to construct a proper foundation for the PVC pipe. <br />2. Boggy soils could extend to a distance of several feet beyond the existing old siphon <br />alignment. <br /> <br />PRB Ditch Company <br />Siphon Replacement Feasibility Study <br />May 2003 <br /> <br />Page 10 of 15 <br />